Flickering head lights, what am I missing

Electrical and Ignition

  1. my68barracuda

    my68barracuda Well-Known Member

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    Went through several of the flickering head light threads, a common solution is to add a relay to get solid voltage to the VR. I was ready to do that, went I went through my wiring I already have a direct line from the battery to the VR. I have a rear mounted battery with a disconnect switch that does kill the motor when it is tripped to off. Although I do see a down side of my setup, the alternator has 12v to it all the time the disconnect is set to on. Is that a problem?
    But I also have a lot of flicker in the lights that I would like to fix.
    New battery made no difference.
    The wire from the alternator to the battery disconnect is a 18 g wire ,(what I labeled as Wire A) when I checked it at the wire connector to the alternator ( the wire disconnected from the alternator) I got 12.75, the same as the voltage across the battery terminals.
    The battery disconnect is a 4 post unit.
    341E6C8F-40E4-4499-A194-0861BC6EE3E5.jpeg
     
    Last edited: Mar 20, 2020
  2. Demonic

    Demonic Well-Known Member

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    An 18ga wire? What is on the output stud of the alternator? Not an 18 ga wire.

    It might be the headlight harness. Add a relay to power the headlights from the battery. You'll need one for the high beams also. The original wires energize the relay coils.
     
  3. Dfr360cuda

    Dfr360cuda MAGA Again

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    Grounds ?
     
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    • R4Sedan

      R4Sedan Larry FABO Gold Member

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      I was thinking a ground or could be your high beam switch.
       
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      • BigBlockMopar

        BigBlockMopar BigBlockMember

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        Headlights behind a relay doesn't fix them flickering.
        The flickering comes from twitchy VR operation and low power-output from the alternator.
        Stock alts are known for that.

        Install a newer (80s/90s) kind of alternator with built-in VR and your flickering is gone.
         
      • my68barracuda

        my68barracuda Well-Known Member

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        Output stud of the alternator?
        the out put stud of the alternator has a 4 G wire that goes directly to the starter relay stud.
        The starter relay stud has a 4G wire that goes to the starter stud,
        The starter stud has a 2G cable that goes to the rear battery disconnect, then another 2G to the battery.

        Grounds
        battery negative post to the starter mounting post is a 2G cable
        starter mount post to a stud on the fender is a 12 G wire, and at the stud is where I ground the voltage regulator, and other misc grounds
        I have the headlights, ECU, Fuel Pump, electric fan all on relays
         
      • my68barracuda

        my68barracuda Well-Known Member

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        I have a newer style Mitsubushi alternator that uses the external mopar regulator
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        Well there's all sorts of stuff that's described as 'flickering' so not enough to even guess about.
        If its at slow idle, and just slow idle - then narrow down if its just when restarting or after a long run.

        As far as the alternator to battery wiring.
        The voltages you measured are battery voltage. Good numbers for a battery.
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        There's the most likely cause - assuming its only at slow idle speed.
        Voltage is rising and falling because the alternator can't supply that much power at 14ish Volts.
        So voltage drops down until it equals battery voltage.

        Bring the rpms up, or increase the load and it will stabilize.
        Don't do that second test for a long time.
         
      • my68barracuda

        my68barracuda Well-Known Member

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        Photo of alternator

        E9927077-D56A-40E1-994A-C30F4A602838.jpeg
         
      • my68barracuda

        my68barracuda Well-Known Member

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        this is 90 amp alternator, wiring has been upgraded, running all the new accessories through relays,
        the flickering is at idle and at higher RPMs, obviously the fuel pump and MDS draw are always present when the motor is running, having the electric radiator fan running or not has no impact on the flickering.
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        Rating indicates approximate maximum output. It doesn't tell us what it can produce at idle rpms. That's a problem with the ratings.
        Some higher output alts can produce more power at idle rpms, and some can't. That type of alternator should be pretty good at lower rpm.
        That's good, but won't help if the available power at 14.x is maxed out.
        Since it continues into higher rpms, that would suggest something other than power to the headlight circuit being limited than the alternator's capacity at idle.
        Might not hurt to put a meter on while running. If a diode is out, or a winding is broken, capacity to produce power will be down and ripple will increase. The latter would show on a oscilliscope - which is not a common tool these days...
         
      • my68barracuda

        my68barracuda Well-Known Member

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        thanks, I will pull the alternator and get it tested,,,
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        To answer the other question. Yes, withthe wiring as shown, as long as the cutoff switch is on, the blue wires will be at battery voltage.
        upload_2020-3-20_16-6-48.png
        If the regulator is calling for power, then the green wire will be connected to ground. In that case current will be be flowing through the alternator's rotor windings. In that case, the green wire will be something less than battery voltage - maybe close to zero. Otherwise it too will be at battery voltage.
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        There is another possibility. The one Demonic mentioned.
        The field windings may not be getting enough power, or at high enough voltage due to the long route and 18ga feed.
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        That alternator probably uses at least 3 or 4 amps when making a strong magnetic field. Could be more like 7 amps.
        That's a long path for 7 amps through 18 gage wire coming from the battery in the trunk. Even longer when coming from the alternator.
        upload_2020-3-20_16-23-31.png
        Arrows represent the current to power the rotor.
        Blue wire to the regulator is mostly to measure the voltage and only takes a fraction of an amp to control the internal switching.
         
      • Mattax

        Mattax Just the facts, ma'am FABO Gold Member

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        A test for that would be to measure votlage difference between alternator out and field terminal feed while the engine is running.
        upload_2020-3-20_16-29-23.png

        And more directly focused on the 18 gage wire, if you have enough wire for the leads.
        upload_2020-3-20_16-34-17.png
         
      • my68barracuda

        my68barracuda Well-Known Member

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        those are some good possibilities, give me a chance to digest these diagrams and I will get back
         
      • cudascott

        cudascott Now I have a Hemi

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        Check the bulkhead connections
         
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        • famous bob

          famous bob mopar misfit

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          This is why we completely rewire these old cars, I didnt want 52 yr old wireing in mine ..
           
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          • Dana67Dart

            Dana67Dart Like a fine wine, only getting better with age! FABO Gold Member

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            Just a thought. A alternator with a bad diode or two might produce a similar situation. Before you pull it swing by the auto parts store and have them put their tester on it in the car. They can detect a bad diode
             
          • my68barracuda

            my68barracuda Well-Known Member

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            the wiring has been upgraded, bulkhead connectors bypassed for the main power feed, dash voltage regulator swapped for a volt meter,,,,,,everything of consequence runs through relays,,, as mentioned in post #11

            a question here, with a car at idle, good charge on the battery and a digital multimeter probing the battery terminals, how much of a voltage swing would you expect to see?
            and the same question with the motor at say 2000 rpm?
             
          • my68barracuda

            my68barracuda Well-Known Member

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            Mattax,, thanks for the very clear diagrams
            but I have a question,
            using a multimeter to measure DC 12 V, would I actually get a reading with one probe on the alternator out and one probe on the field terminal indicated?
            same question when probing from the field terminal to the disconnect,,,

            I thought there had to be a flow potential, for example from a positive to a ground to measure voltage.
            or are you saying to measure from the alternator output to ground then the field terminal to ground?
            I don't know just asking.
            I did similar with the engine not running and got battery voltage at the field terminal alternator connection.
            I have a DC clamp amperage meter, tomorrow I can check flow through that wire, or maybe I will just rig up a temporary 12 foot splice the length of the 18 g wire to see if that impacts the flickering.
             
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            • Mattax

              Mattax Just the facts, ma'am FABO Gold Member

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              cool-gif.gif
              Totally cool. You're on the right track.

              In theory there would be no reading from either.
              In reality there may be a voltage drop in either or both portions of the circuit.

              Can also measure it that way. If the ground circuit is real good, the results will be the same.
              Lets say the measurement from the alternator output stud to the field terminal shows a drop of 0.5 Volts.
              Measuring the stud to ground and the field terminal to ground should result in readings that are .5 Volts different.

              Yes.
              When it is just potential and there is no current flowing, voltage of everything connected to the battery positive will be the same.

              Things can change a little when current is flowing. Anything that causes resistance to that flow creates voltage drops.

              By measuring the voltage from one point along the supply to another point in the supply we'll know if there is resistance to the flow. In this case we'll know if that 18 gage wire is too small for the distance and amount of current.

              If it helps, think of amperes like gallons per minute, and volts like psi. If there is resistance to the gal/min, then the pressure at the other end of the system won't be the same as at the beginning. But if nothing is flowing, pressure is the same throughout the system.
               
            • 67Dart273

              67Dart273 FABO Gold Member FABO Gold Member

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              The FIRST thing I'd do is upgrade that 18 ga wire in the field/ regulator circuit. One thing you need to realize is that the VR/ field circuit PULSATES and one reason it is not normally noticeable is that the inductance of the alternator field itself sort of averages that out. However, with a long run of too-small wire, you can set up interesting feedback/ oscillations type of deal. The VR power (IGN) terminal MUST "see" "same as battery" to regulate correctly that IS the sensing terminal.

              In fact, I see no reason to wire it the way that you did. If you use the small terminals of a 4 terminal (double pole) disconnect to control a relay in conjunction with an ignition switch, you can then pull power for ignition/ field / regulator off the large main feed "up front" and eliminate voltage drop problems
               
              • Thanks! Thanks! x 1
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